Biomedical Engineering Reference
In-Depth Information
acts as proton donor in polymerization. Figure 3.4 shows cyclic
voltammograms of the growing PANI film in both aqueous and IL
solutions. The polymerization rate was found to be much slower
in [EMIM][OTf ] than in aqueous solution, and therefore, increased
concentration of the monomer was used. Also the current response
during potential scanning was lower in IL than in the aqueous
electrolyte. The films made by potential cycling in [EMIM][OTf]
are, however, smoother than the films made in aqueous solution
and they also exhibit higher conductivities. Li et al. synthesized
the IL 1-ethylimidazolium trifluoroacetate ([EIM][TFA]) with high
yield and used it as the electrolyte in polymerization of PANI [64].
Polymerization rate in this IL was higher than in sulfuric acid.
Additionally, the films made in [EIM][TFA] had high electrocatalytic
activity to oxidation of formic acid. Cycling the PANI film in this
IL for 300 scans did not show any significant decrease in the
electrocatalytic activity of the film. Morphological studies showed
that the films made in [EIM][TFA] were smoother than the films
made in sulfuric acid. The authors claim that the enhancement in
polymerization is due to the high viscosity of the used ionic liquid.
Polymerization of PANI in ionic liquids was also made by Wei et al.
[65]. Nanotubular structures of PANI were obtained on modified ITO
glass by using [BMIM][PF
] mixed with 1M trifluoroacetic acid. The
electrosynthesis resulted in the emerladine form of PANI. Potential
cycling to 50 scans indicate continuous growth of PANI film in IL
acidic solution and the SEM analysis show tubular structure of PANI
with a diameter of ca. 120 nm.
Conducting polymers, based on polyphenylenes have intensively
been studied due to their interesting electroluminescence property
[66, 67]. However, PPP is unstable and also the synthesis is
problematic due to the humidity sensitivity of the polymerization
process. To overcome these problems, ILs can be applied. Endres and
coworkers used moisture-stable ionic liquids for electrosynthesis
of benzene [68, 69]. They used 1-hexyl-3-methylimidazolium
tris(pentafluoroethyl) trifluorophosphate in electrosynthesis of
PPP. The EQCM studies in that work showed incorporation of anions
from the IL and a significant cation exchange in order to preserve
electroneutrality in the film, resulting in porous PPP structures.
Electrochemical polymerization of PPP from biphenyl in ILs was
6
Search WWH ::
Custom Search